implementing Integer Overflow When Manipulating Large Arrays in C using Dynamic Allocation
I'm having a hard time understanding I'm relatively new to this, so bear with me. I've looked through the documentation and I'm still confused about Quick question that's been bugging me - I am working on a C program that processes large arrays of integers but I am working with issues with integer overflow, especially when dynamically allocating memory for larger data sets... I have a requirement to populate an array with a size based on user input and then perform operations that involve calculating the sum of its elements. However, when I input a size that is too large (e.g., over 1 million), the program behaves unexpectedly. Here’s the code snippet where I allocate the array and calculate the sum: ```c #include <stdio.h> #include <stdlib.h> int main() { int n; printf("Enter the number of elements: "); scanf("%d", &n); // Dynamic allocation of array int *arr = (int *)malloc(n * sizeof(int)); if (arr == NULL) { fprintf(stderr, "Memory allocation failed\n"); return 1; } // Populating the array for (int i = 0; i < n; i++) { arr[i] = i + 1; } // Calculating the sum long long sum = 0; // Use long long to store the sum for (int i = 0; i < n; i++) { sum += arr[i]; } printf("Sum: %lld\n", sum); free(arr); return 0; } ``` When I run the program with an input size of 1000000, the sum calculation seems to work fine, but for sizes like 2000000, I notice that the sum output is incorrect, and sometimes it prints negative values. I suspect it might be due to integer overflow since I’m using an `int` for indexing and that should theoretically allow for larger values. However, I thought using `long long` for the `sum` variable would prevent overflow. I also checked the values being added to `sum`, and they seem reasonable, yet the final result is off. Additionally, I’m on GCC version 11.2.0 on an Ubuntu 20.04 system. What could be causing this scenario, and how can I fix it to handle larger arrays safely? Am I missing something in my allocation or sum calculation? This is part of a larger API I'm building. This is part of a larger application I'm building. Am I missing something obvious? Has anyone else encountered this? I'm using C 3.9 in this project. What am I doing wrong? The project is a application built with C.